Centralizer

ABSTRACT

The new centralizer for well casings consists of a pair of collars connected by bowed leaf springs of different curvature and in stacked or side-by-side arrangement for increasing the resistance of the bows to radial bending and for increasing the radial extent of the centralizer.

United States Patent Hall, Sr. 1 Feb. 22, 1972 [54] CENTRALIZER 2,605,844 8/1952 Clark ..166/241 2,636,564 4/1953 Kluck v ..166/241 [721 2,656,890 10/1953 Brandon ..166/241 [73] Assignee: Weather-ford Oil Tool Company, Inc.,

Houston Primary ExaminerDavid H. Brown [22] Filed; Se t,6, 1966 Attorney-Bertram H. Mann, Frank B. Pugsley, James G.

U1 1 pp No: 577,364 mer DelmarL Sroufe and RobertA White [52] U.S.Cl ..l66/241, 166/173 [57] ABSTRACT [51] Int. Cl ..E2lb 17/10 The new centralizer for well casings consists of a pair of col- [58] Field of Search ......166/ 172, 173, 213, 241, 202; lars connected by bowed leaf springs of different curvature 308/4 A; 15/ 104. 19 and in stacked or side-by-side arrangement for increasing the resistance of the bows to radial bending and for increasing the [56] References Cited radial extent of the centralizer.

UNITED STATES PATENTS 6 Claims, 8 Drawing Figures 2,368,737 2/ 1945 Badgley ..166/241 X /i\ 9 zs T or &

PAIENTED FEB 2 2 I972 SHEET 1 []F a r. y M M /m l A. M A E w M PAIENIEHFEBZZ 1912 3.643 739 sum 3 0F 4 dab/7 A. Haw/L, Jr.

INVENI'OR.

ATTORNEY CENTRALIZER This invention relates to centralizers for properly spacing from the wall of a borehole in the earth a pipe projecting into the hole as for surveying or cementing or other purpose.

In the case of very large holes bored in the earth, for instance, for mine shafts or wells of various types, it is frequently necessary to cement or otherwise protect and/or seal the bore walls. In cementing techniques, a casing is run in the borehole, then cement slurry is supplied through the casing, usually, in larger boreholes, through separate pipes, thence through a shoe at the bottom of the casing and then upwardly into the annulus between the casing and bore wall. Upper portions of the annulus may be cemented through separate pipes run outside the casing or welded to the outside thereof.

In order that a fairly uniform cement fill be provided for protective and sealing purposes in the annulus, it is desirable to maintain the casing a substantially uniform distance from the bore wall, and this is conventionally achieved by means of centralizers which are mounted on the casing. A conventional centralizer of the type now in general use consists simply of a pair of collars received about the' casing and bridged by longitudinal or helically inclined, outwardly bowed leafsprings or wires. The collars may be slidable, at least to a limited extent, on the casing to permit reciprocation and/or rotation of the latter together with scratchers or wipers secured to the casing for conditioning the bore wall prior to cementing. Alternatively, these centralizers may be rigidly secured to the casing, as by welding or glueing, or by stop collars fixed mechanically to the casing and fixed to the centralizer collars or made as a part thereof.

However, where the hole or shaft is extra large or a very thick annular cement fill is desired, it has been necessary to longitudinally extend centralizers of the conventional type to such an extent that they become too bulky and heavy for easy handling by workmen in running the casing and, possibly, too long for mounting on a single casing section of the type often used in big holes. On the other hand, where the centralizer does not sufficiently span the space between the casing and the well bore wall or the cavity walls, separate cement-delivering pipes, run after the casing is in position, may not be properly separated and guided to their separate places between the springs of each centralizer.

Another difficulty with presently known types of centralizers is that the initial resistance of the spacing bows to bending is so small that, particularly in slim holes, desired minimum clearance between the pipe and borehole walls is not maintained.

Consequently, an object of the present invention is to provide a centralizer, particularly for large boreholes or shafts, which can be easily handled and installed by workmen in the field.

Another object is to provide improved means for guiding and separating individual pipes run between the casing and the well bore, as for feeding gravel, cement, or other fluent material into different sections of the hole.

Another object is to provide a centralizer adapted to slide along the bore wall during running of the casing and which will reach into enlarged wall cavities so as to prevent a fluid pipe being run between the casing and bore wall from being diverted, for instance, through such cavity, from its intended path in a trough between adjacent centralizer wings and in alignment with the casing.

Another object is to provide means in a centralizer having radially stacked bow springs for directing the cement through and around the springs and along the casing and bore walls.

Another object is to provide a large hole type of centralizer which is ofa practical length to be mounted singly or in multiples on a single section ofcasing.

Still another object is to provide a bow-type centralizer of greater radial resilience than previous centralizers and a novel method of constructing the same.

These objects and others hereafter appearing are attained substantially by the devices illustrated in the accompanying drawings in which FIG. 1 is a view of an exemplary form of the novel centralizer inserted in a borehole, part being shown in elevation and the remainder in longitudinal section;

FIG. 2 is an enlarged perspective view of a detail showing the means for mounting the superposed springs on underlying springs;

FIG. 3 is an end view of the device in FIG. 1, taken substantially on line 3-3 thereof;

FIG. 4 is a view similar to FIG. 2 showing a modification;

FIG. 5 is a half-elevation of a length of casing having another modified centralizer thereon;

FIG. 6 is an exploded half-elevation of the structure in FIG. 5 and illustrating the method ofassembling the same;

FIG. 7 is an end view of another modification; and

FIG. 8 is an elevation of still another modification, parts being broken away.

The form in FIGS. 1-3 includes a plurality of coaxial collars .8, 9, l0, and 11 adapted to be received about a casing section 12 and which comprise the cylindrical body structure of the device. The casing is run into a large size borehole or shaft 13 having a cavity 14 in one side, in this instance, a key slot. Each adjacent pair of collars is bridged by an annular series of outwardly bowed straps or leaf springs 15, 16, and 17, the ends of which are welded to the collars, but may be otherwise secured thereto. Each of the innermost or base straps or springs l5, l6, and 17 is arranged longitudinally and, preferably, one spring in each annular series is longitudinally aligned with corresponding springs in adjacent series to form, in effect, a vertical row. As shown in FIG. 3,'eight such longitudinal rows are provided around the body structure, although any convenient number may be provided, preferably, of course, symmetrically. Also, one end of each of the springs 15, 16, and 17 may be slidable upon itsmounting collar.

Mounted upon each adjacent pair in a longitudinal row of the springs or straps l5, l6, and 17 is an intermediate leaf spring, as 18 and 19, the ends of each latter spring being mounted intermediately on the underlying springs. Secured to the ends of the intermediate springs, as by welding, are clamping brackets, as 20, 21, and 22, one of these being shown enlarged in FIG. 2. The legs of these brackets are folded, as at 23, under and against the centers of underlying springs. Stop lugs 24 and 25 are welded to the end underlying springs 15 and 17 immediately inwardly of brackets 20 and 22. Central bracket 21, which embraces the adjacent ends of both intermediate springs '18 and 19, may be welded, also, to support spring 16. Conveniently, intermediate springs l8, 19 are held initially under slight tension by stop lugs 24 and 25.

Mounted upon each longitudinal pair of intermediate bow springs 18 and 19 is a third annular series of spring straps 28 which centrally engage portions 13 and 14 of the bore wall.

Right-hand spring strap 28 in FIG. 1 is shown as extending into a cavity, as of the key seat type, while the left-hand outermost spring is shown as engaging a portion of the bore wall 13 of normal diameter so as to substantially flatten this spring and cause clamping brackets 29 and 30, folded about intermediate leaf springs 18 and 19, to separate from stop lugs 31 and 32. The corresponding intermediate springs 18 and 19, which cooperate to support outermost spring 28, are flattened to a lesser extent, while the innermost leaf springs 15, 16, and 17 are only slightly flattened if at all. In fact, it is contemplated that the resilience of the successive stacked rows of leaf springs may be decreased outwardly so as to bear more lightly against the borehole wall, yet be free to flex into cavities.

In the form in FIG. 4, rigid semicylindrical sections 34, tubular or solid, are substituted for the innermost leaf springs 15, 16, and 17 in the first form, while intermediate springs 35 and outermost springs 36 are superimposed thereon in radial stacking.

FIG. 1 also shows a pair of stop collars 38 and 39 of any suitable form secured to the casing or pipe 12 between the endmost collars 8 and 9 and 10 and 11. The vertical rows of stacked leaf springs provide segmental channels or troughs 41 therebetween (FIG. 3) through which are extended pipes 42,

for instance, for delivering cement slurry to the well annulus or for other purpose. These rows of springs serve to guide the piping downwardly into the borehole, such guiding being effective even in the vicinity of substantial cavities, as at 14, which previous centralizers have not been able to enter.

In order to prevent channeling of the cement flowing upwardly along the centralizers and to cause the cement to fill the spaces about the centralizers, guiding or diverting fins may be attached to any number of the bowed springs, as at 43, 44, and 45. One of these is shown enlarged in FIG. 2. The fins are secured by suitable means to the straps and project sidewardly of the straps and are of suitable size and shape to catch and divert the upflowing cement through the loops formed between the springs and/or selectively against the casing and the bore wall. The laterally projecting edges of the fins, preferably, should be curved to prevent catching of pipes being run into the annulus about the casing and centralizers. While only a few of the springs are shown in FIG. 1 as being equipped with the fins, the fins may be otherwise placed and disposed as desired.

The centralizer, of radially stacked spring elements, may be specially made up to match a particular hole size, although with proper tools the assembly could be achieved wholly or in part in the field. Other stacking arrangements may be utilized as, for instance, the stacking ofintermediate and outer springs upon a single base or inner spring, and the device may be extended laterally as needed by further stacking or reduced by elimination of the outermost springs. In some cases, it may be convenient to build the device on several conventional centralizers, as heretofore referred to. By laterally extending the centralizer by means of stacked spring elements as herein disclosed and claimed, the unit may be made sufficiently light and compact to be handled by installation workers and will not be too long to be mounted singly or in multiples on a single casing section. While the longitudinal alignment of the stacked springs provides channels for running and segregation of supply pipes, as at 42, the springs may be helically disposed.

In case increased radial rigiditY is desired, both ends of all of the bows, or of a part thereof, may be nonmovably secured to the underlying supporting structure. This will have the effect of accumulating the radial resistance of the bow assembly so as to more strongly resist approach of the pipe and bore walls. Other designs for achieving such radial strengthening, e.g., increased radial resilience, are shown in FIGS. 5-8.

FIGS. 5 and 6 illustrate another modified stacking arrangement including a prestressing assembly method. A pair of split collars 50 and 51 are secured about the casing section 52 on opposite sides of a stop collar 55 as by pin and eye hinges 53 and 54. The collars are secured together by stacked pairs of bowed spring straps 56 and 57, 56a and 57a, 56b and 57b, etc., preferably but not necessarily symmetrically disposed, as in the previous form. However, the bows of each pair are of different curvature and are welded together at their ends and welded or otherwise firmly secured to the collars so as to withstand forces set up when the centralizer is dragged in both directions through a well bore.

FIG. 6 illustrates a method of assembly which prestresses the bows, providing still greater initial resistance to radial compaction, as may be desirable, particularly in close tolerance installations. First, all of the set of inner bows 57, 57a. 57b, etc., of lesser curvature are secured to the collars and then radially compacted, as by a split collar 60 clamped about the mid portions of the bows. This has the effect of slightly straightening these bows (reducing their curvature) and increasing the distance between the collars 50 and 51. Outer bows are selected of such length that their ends are initially spaced farther apart than the ends of the unstressed inner bows. These longer, preferably unstressed, outer bars are then welded to the stressed inner spring bands, as in FIG. 5. Stressing clamp 60 is then removed, whereupon the inner bows tend to resume their unstressed shape and to draw together end collars 50 and 51. This action is resisted by the outer bows which are, accordingly, themselves placed and held under bending stress.

The pairs of spring bows assembled as shown produce a centralizer which offers substantially greater resistance to radial compaction upon contact with a bore wall 61 than previous centralizers having single bow springs even where such springs are substantially wider or thicker than the springs conventionally used in this type of centralizer. This is because the inward radial reaction applied to the .centers of outer set of bows 56, etc., as symbolized by the arrow 62, is resisted not only by the inherent resistance to bending of the outer set of bows but, in addition, by the resistance offered by inner set of bows 57, etc., to separation of end collars 50 and 51, e.g., the longitudinal resilience of the inner set. This latter resistive force, applied longitudinally at the ends of the inner bows, is greater because of the moment arm involved than would be the resistance to bending which these inner bows could offer to centered radial forces applied as at 63. The prestressing of the bows tends to increase the initial resistance to radial compaction, as explained.

If desired, resilient or flow-diverting elements may be interposed between the inner and outer elements of the pairs, as indicated at 64 or at 43, 44 in FIGS. 1 and 2. Advantages of increased radial stiffness could also be obtained where sets of bows are not stacked as in FIGS. 5 and 6, but rather are individually secured to the end collars, for instance, in alternate arrangement. FIG. 7 shows such further modification wherein alternate bows 65 and 66 conform in length and curvature, respectively, with outer and inner spring straps 56, etc., and 57, etc., of FIG. 5. These bows may be constructed so that, after release of the prestressing means, as the split collar 60 of FIG. 6, all bows will be of uniform curvature so that all will bear against an encompassing cylindrical bore wall. In any case, the resistance of one set of bows to radial compression (represented by the arrow 62) and accompanying elongation will be strengthened by the resistance of the other set of bows to elongation. The bows may be constructed of compound curvature, that is, with S-bends, as at 72 in FIG. 8, or with multiple apices and intervening cusps. Also, in the arrangement of FIG. 7, or in an arrangement where all bows extend substantially the same distance radially of the centralizer, one or more of the bows may be shortened-that is, their end portions which are secured to the collars may be closer together axially than the corresponding ends of others. Such shortened bows are stiffer, e.g., more resilient, longitudinally and serve to increase the radial stiffness of the centralizer, as explained above.

FIG. 8 shows still another modification in which an inner set of members 70, either paired in stacked relationship with bowed outer set of straps 71, or staggered as in FIG. 7, extend longitudinally, without bowing, and are provided with S- shaped or other longitudinally resilient sections, as at 72. The inner, longitudinally resilient set of members functions to resist separation of end collars 73 and 74, as do the inner straps in FIG. 5. Both sets of members, preferably, are prestressed and may be bowed, as in previous forms, and may extend helically.

An advantage in the stacked arrangement of bow springs, as in FIGS. 1 through 6, is that, upon possible reverse flexing of the outer bows, due to excessive radial forces applied thereto, such flexing will be limited by the underlying bows.

The invention may be modified in these and other respects as will occur to those skilled in the art, and the exclusive use of all modifications as come within the scope of the appended claims is contemplated.

Iclaim:

1. A centralizer comprising a plurality of collars disposed coaxially for reception about a pipe insertable in an orifice, first bowed leaf springs connecting said collars, and other bowed leaf springs with their ends mounted on said first springs intermediately thereof.

2. A centralizer as described in claim 1 in which at least one of said other leaf springs is radially stacked on at least one of said first springs.

3. A centralizer as described in claim 2 further including fin elements projecting from at least some of said leaf springs for diverting materials flowing therepast.

being arranged in longitudinally aligned groups with each spring of a group connecting an adjacent pair of collars.

6. A centralizer as described in claim 5 further including third leaf springs superposed respectively on said other leaf springs.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3 .643 739 Dated February 22 1972 Inventofls) John A. Hall, Sr.

It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

In column 5, line 1, claim 4, reading "A' centralizer as described in claim 3 in which said first" should read A centralizer as described in claim 1 in which said first-.

Signed and sealed this 6th day of June 1972.

(SEAL) Attest:

EDWARD M.FLETCHER, JR. ROBERT GOTTSCHALK Atte sting Officer Commissioner of Patents FORM PC4050 (10'69) USCOMM-DC 60376-3 69 U.S GOVERNMENT PRINTING OFFICE 1 I959 O356334 

1. A centralizer comprising a plurality of collars disposed coaxially for reception about a pipe insertable in an orifice, first bowed leaf springs connecting said collars, and other bowed leaf springs with their ends mounted on said first springs intermediately thereof.
 2. A centralizer as described in claim 1 in which at least one of said other leaf springs is radially stacked on at least one of said first springs.
 3. A centralizer as described in claim 2 further including fin elements projecting from at least some of said leaf springs for diverting materials flowing therepast.
 4. A centralizer as described in claim 3 in which said first leaf springs are arranged in longitudinal groups and each of said other leaf springs is mounted on intermediate portions of a pair of said first springs.
 5. A centralizer as described in claim 4 in which three or more of said coaxial collars are provided, said first leaf springs being arranged in longitudinally aligned groups with each spring of a group connecting an adjacent pair of collars.
 6. A centralizer as described in claim 5 further including third leaf springs superposed respectively on said other leaf springs. 